The present invention relates to a hand-held electrically powered hammer tool with a rotor-type electromotor and a hammer mechanism arranged in a machine housing, said hammer mechanism including a drive shaft with an excentric crank pin thereon for a piston rod connected to a drive piston reciprocably movable in a cylinder for driving a hammer piston towards a tool via an elastic means in a working chamber of said cylinder between said pistons.
Hammer tools of this type are known which have a gearing between the electromotor and the hammer mechanism. The gearing has enabled the high-speed series commutator motors previously used to develop a sufficient torque for driving the hammer mechanism without need of being too powerful and heavy which is particularly important for hand-held equipment. The total driving assembly including the gearing will, however, become rather spacious and heavy especially for tools in the high-power range. The gearing is also complicated and expensive to manufacture and often cause working interruptions due to overheating of unsufficiently lubricated gear parts. An additional drawbck with these known hammer tools is that the electromotors have spark producing brushes which may be hazardous in inflammable or explosive atmosphere. The brushes and commutator are also exposed to hard wear since the drill dust reaches these parts.
An object of the present invention is therefore to provide a hammer tool which does not possess the above drawbacks and has a lower weight-to-power ratio than similar machines of prior art and which has a more simple and robust construction.
This object and others are achieved by providing a hammer tool according to the accompanying claims.